Electronic tongue as ozone detector

ABSTRACT

An electronic tongue for the detection of ozone is based on voltammetry, and comprises at least one working electrode and a counter electrode, wherein the working electrode(s) is(are) made of one or more transition metals or Au, or alloys thereof, or alloys thereof with other metals. The data processing is made by multivariate analysis. The sensor can be implemented on-line or in-line in a processing plant where it is desirable to monitor and control ozone levels, e.g. sterilization and purification plants.

[0001] The present invention relates to detectors of the type commonlyreferred to as electronic tongues, and in particular to an electronictongue based on electrochemical detection, for the detection of thepresence of ozone and measurement of its concentration in a liquidsample.

BACKGROUND OF THE INVENTION

[0002] The control of ozone levels in the ppm range is a very importanttool i.a. for the sterilization of materials, e.g. preparations formedical use, equipment and apparatuses, where ozone is used foreliminating harmful and unwanted species. Ozone is a substance withexcellent qualities to kill microbiological entities such as virus,bacteria, spores and fungi. As ozone is toxic to these entities alreadyat low concentrations (ppm-range) it is imperative to be able to controland measure ozone on-line in real time. Such a method would be highlyvaluable for cleaning, disinfection and sterilization of various typesof equipment and processes, such as medical devices, food and beverageprocessing equipment as well as in agriculture and breedingenvironments. The method could also be used for measuring the oxidationof organic material in the development and manufacturing ofmicroelectronic products and production methods.

[0003] Ozone detectors according to prior art have been based on anumber of different methods. Most methods require use of some kind ofreagent, which means that either a sample must be withdrawn from thesystem in which the ozone is to be determined, or one has to accept acontamination of the system. The latter is unacceptable in e.g.sterilization of water for medical purposes. Spectroscopic methods wouldnot cause such interferences, but requires fairly complex systems thatare expensive. Also, they require the provision of windows in the lightpaths, where clogging can occur causing drift problems over time.

[0004] In WO 99/13325 there is disclosed an electronic tongue based onelectrical pulses according to a pulse programme comprising a pluralityof pulses in sequence and at different amplitudes, being applied toelectrodes. The electrical pulses are i.a. selected from voltage pulsesand current pulses. The obtained response signals are used as input to apattern recognition program in a computer for interpretation and foroutputting results indicative of a desired property of a sample, such asthe concentration of an analyte, pH etc. The analysis is based onmultivariate methods, such as PCA (Principal Component Analysis). Abrief account of PCA is given in an article by F. Winquist et al in “Anelectronic tongue based on voltammetry”, Analytica Chimica Acta, 357(1997) 21-31. This article and the WO publication are both incorporatedherein in their entirety by reference.

SUMMARY OF THE INVENTION

[0005] The present inventors have now conceived a new application of anelectronic tongue of the type discussed above, namely for detection ofthe presence of and the measurement of the concentration of ozone in aliquid sample.

[0006] The invention in a first aspect comprises an electronic tonguefor the detection of ozone, based on voltammetry, comprising at leastone working electrode and a counter electrode, wherein the workingelectrode(s) is(are) made of one or more Rh, Pt, Au, Os, Ru, Ni, Ti, Re,or alloys thereof, or alloys thereof with other metals.

[0007] A system incorporating the inventive tongue comprises an ozonedetection system based on voltammetry, for detecting the presence and/orconcentration of ozone in a liquid sample, comprising at least oneworking electrode made of one or more transition metals or Au, or alloysthereof, or alloys thereof with other metals; a counter electrode; aprogrammable pulse generator capable of applying a redetermined sequenceof energizing pulses to said working electrode(s); a recording devicefor recording the output from said working electrode generated inresponse to said applied pulse sequence; a sampling device for samplingvalues of said output at predetermined intervals; a memory for storingsaid sampled values in a matrix; a processing unit (PC) for performing amultivariate analysis of said data matrix; and a display device fordisplaying the result of said multivariate analysis.

[0008] The electronic tongue of the invention is based on voltammetry,and on a specific selection of metal(s) or metal alloys for the workingelectrode.

[0009] Advantages with the invention are i.a. the simplicity of thesystem, it is long term stable. In particular, it is possible to operatethe system without a reference electrode. Thereby any risk ofcontamination of the system to be monitored with leaking electrolytefrom a reference electrode is eliminated. Also, regular replacement ofthe reference electrode is eliminated.

[0010] Such replacement would otherwise have to be done at regularintervals, and adds further to the overall cost.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The invention will be described in detain below with reference tothe drawings, in which

[0012]FIG. 1 shows a typical experimental setup for using the presentinvention;

[0013]FIG. 2 shows an embodiment of a sensor device incorporating theinventive idea;

[0014]FIG. 3 shows a pulse sequence usable with the invention;

[0015]FIG. 4 is a PCA plot of a typical ozone measurement;

[0016]FIG. 5 shows correlation between measured and predictedconcentration values determined according to the invention;

[0017]FIGS. 6a-d are PCA plots of measurements made with differentsingle electrodes;

[0018]FIG. 7 is a PCA plot of a measurement based on a four-electrodesensor with different metals as electrodes;

[0019]FIG. 8 shows an alternative embodiment of a sensor according tothe invention;

[0020]FIG. 9 shows still another embodiment of a sensor according to theinvention;

[0021]FIG. 10 schematically illustrates an implementation of aninventive sensor in a sterilization equipment;

[0022]FIG. 11 is a schematic illustration of a LAPV stair case; and

[0023] FIGS. 12-18 are graphs showing measurements with a number ofelectronic tongues.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0024] For the purposes of the present invention the term “electronictongue” shall be taken to mean a device comprising at least one sensingelement, the response of which on stimulus from a sample is processedwith multivariate methods. A “sensing element” can be any one of aplurality of devices, such as, but not limited to, electrodes at thesurface of which redox reactions take place.

[0025] The invention will now be described with reference to oneembodiment using a voltammetric system, and a setup of this type isshown in FIG. 1. The setup includes a sample reservoir 2 containing asample, the ozone concentration of which is to be determined. Thisreservoir can be of a stationary type or designed as a flow cell, in theexperiments described below a stationary cell with a magnetic stirrer 4is used. A sensor device 6 is immersed in the sample liquid. Theillustrated embodiment of the sensor device, shown in FIG. 2, comprisesan essentially rod shaped support structure 8, in which a plurality ofmetal wires or metal pins 10 are imbedded, the ends of which areexposed. The exposed ends of the wires form the working electrodes 12 ofthe sensor device. The support structure is preferably made of amaterial that will ensure a very good sealing between the metal wiresand the material in which they are embedded, in order to eliminate anyinterferences in the measurements due to liquid leaking in between thesupport material and the wire. A suitable material is a dental material,sold under the trade name Komposit™, Filtek™ Z250, obtainable from 3MSvenska AB, Sweden. Of course any other material having the capabilityto provide adequate sealing is usable.

[0026] An Ag/AgCl (KCl 3M) electrode can be used as a referenceelectrode, however other conventional reference electrode well known tothe skilled man are equally well usable.

[0027] The measurement set up can be implemented in several ways. I.a. astandard three-electrode system can be employed, i.e. a workingelectrode, an auxiliary (counter) electrode and a reference electrode.Alternatively only a reference electrode and a working electrode can beused.

[0028] It should be noted however, that the invention works very wellwithout the use of any reference electrode at all. Thus, in a preferredembodiment, a two-electrode set up with a working electrode and anauxiliary electrode is used. The potentials are controlledelectronically and/or with software in the control unit (e.g. apotentiostat).

[0029] In the shown embodiment (FIG. 2) the sensor device comprises 6working electrodes 12, made of different metals. However, the number ofelectrodes is not critical and could range from one single electrode upto several tens of electrodes or even more. The limit is in principleonly set by the number of external connections to be made. It becomesincreasingly difficult if several hundred electrodes are to be connectedto external devices, although it should not be ruled out as apossibility. The metals from which the electrodes are made can beselected from one ore more members of the group consisting of Rh, Pt,Au, Os, Ru, Ni, Ti, Re and alloys thereof, or alloys thereof with othermetals. Any metal that yields the desired effect would of course beapplicable.

[0030] The metal wires extend throughout the support 8 and exits at theopposite end where they are connected to electrical leads 14. As anauxiliary electrode 16 (counter electrode) a tube of stainless steelencloses the rod shaped support structure in a tight fit. If theapparatus or system, in which the invention is implemented, is itselfmade of e.g. stainless steel, the apparatus housing could be used as acounter electrode. Other materials for the auxiliary electrode are ofcourse conceivable, e.g. Pt, Au. An electrical lead 18 is connected alsoto the auxiliary electrode. The electrical leads from all electrodes arecoupled to a potentiostat 20. The working electrodes are couple via arelay box 22 allowing each working electrode to be coupled separately ina two-electrode configuration (without reference), or three-electrodeconfiguration (with reference).

[0031] Current and current transient responses are measured by apotentiostat MA 5410 (ISKRA, Chemel AB, Lund, Sweden) connected via aninterface. An electronic filter with a time constant of 0.3 seconds isapplied to the potentiostat in order to smooth the time transientresponses. A personal computer is used for controlling the system, e.g.the timing of onset of pulses, operation of the relay box, measuringcurrent transient responses and for the storage of data. A computerprogram written in Labview™ (National Instruments) is used to define theapplied voltages on the electronic tongue, to control the samplingfrequency and to define the data points to be stored in a data matrix.

[0032] For the experiments that will be discussed below, a measurementsequence was composed with two types of voltages and two electrochemicalcleaning procedures applied to the electronic tongue. Of course itshould be realized that this is only an exemplary sequence, andvirtually any combination of pulses (amplitude, duration etc) can beused, so long as a useful result can be obtained. Regarding the shape ofpulses, there are many options available, e.g. square/rectangular pulses(as in the example below), sawtooth, sine wave, etc. Also, a fourelectrode (Au, Ir, Pt, Rh) sensor device was used. The sequence used inthe experiments is as follows (illustrated in FIG. 3):

[0033] A: Electrochemical cleaning

[0034] This procedure starts with a positive potential of 1.5 V appliedto a working electrode during 0.5 s. Then a negative potential of 2.1 Vis applied during 0.5 s. Finally the potential is set to 0 V during 2 s.This is repeated for all working electrodes.

[0035] B: Large Amplitude Pulse Voltammetry (LAPV)

[0036] The LAPV procedure starts with a potential of −2.1 V applied to afirst working electrode during 0.5 s. The potential is then dropped to 0V and maintained there for 0.5 s. Again a negative potential, but 300 mVhigher than the first potential, is applied and maintained for 0.5 s,whereupon the potential again is set to 0 V. This sequence is continueduntil a final maximum potential of +2.1 V is reached.

[0037] C: Electrochemical cleaning

[0038] The same procedure as in A is repeated.

[0039] D: Staircase voltammetry

[0040] A potential of −2.1 V is applied to the working electrode, thispotential is maintained for 0.5 s, and is then increased by 300 mV insteps until the final maximum potential of +2.1 V is reached.

[0041] This whole sequence A-D is repeated for each working electrode inthe sensor device, i.e. four in the illustrated embodiment, and isdefined as one cycle.

[0042] The measurement consists in sampling current values from theresponse curve generated as a result of the potential pulse programme.The measurement sequence is divided in 57 steps, each step having aduration of 500 ms. Current values are sampled at a rate of 1000 Hz, andthus each step generates 500 values, of which 19 are selected and storedin a data matrix. The selection of data points can be adapted to thespecific case, and is not critical to the method. It is simply necessaryto reduce the number of points to a reasonable number. However, areasonable number can be very different from case to case. In certaincases perhaps it is sufficient with four points, in other circumstancesof the order of 100 points could be relevant. Consequently, in the aboveexample, for each electrode there will be 19×57=1083 values stored inthe matrix, and totally for all four electrodes 4332 measurement valuesare generated and stored.

[0043] The data processing is done by multivariate analysis, inparticular so-called Principal Component Analysis is used, and will bebriefly discussed below, with reference to FIGS. 4-7.

[0044] Thus, for the example given above where four different workingelectrodes are employed, a measurement consists of performing one pulsesequence for each electrode, which generates a data matrix with 4332values. This matrix can be looked upon as one point in a4332-dimensional space. Then, a new measurement is made, which generatesa new matrix of 4332 values, and finally a set of matrices representinga number of points in 4332-dimensional space has been generated. InTable 1 a full data sampling experiment of 147 measurements is shown,and it will be discussed in some detail, and FIG. 4 is a graphicalrepresentation of the data in Table 1. TABLE I Conc. Conc. Conc. O₃ TempConc. O₃ Temp O₃ Temp O₃ Temp. Cycle (ppm) ° C. Cycle (ppm) ° C. Cycle(ppm) ° C. Cycle (ppm) ° C. 1 0 31 48 3.0-2.9 32 95 2.9-3.0 31 1420.8-0.9 32 2 0 31 49 3.0-2.9 32 96 2.9-3.0 31 143 0.9 32 3 0 31 503.0-2.9 32 97 2.9-3.0 31 144 0.9 32 4 0 31 51 3.0-2.9 32 98 2.9-3.0 31145 2.4-2.9 32 5 0 31 52 3.0-2.9 32 99 2.9-3.0 31 146 2.9-3.0 32 6 0 3153 3.0-2.9 32 100 2.9-3.0 31 147 2.9-3.0 32 7 0 31 54 3.0-2.9 32 1012.9-3.0 31 148 8 0 31 55 3.0-2.9 32 102 2.9-3.0 31 149 9 0 31 56 3.0-2.932 103 31 150 10 0 31 57 3.0-2.9 32 104 2.0 31 151 11 0 31 58 2.5-1.9 32105 31 152 12 0 31 59 1.9-1.6 32 106 31 153 13 0.7-2.2 31 60 1.6-1.3 32107 1.5 31 154 14 2.2-2.6 31 61 1.1-1.0 32 108 31 155 15 2.6-2.8 31 621.0-0.9 32 109 31 156 16 2.9 31 63 0.9-0.8 32 110 1.2 31 157 17 2.9 3164 0.8-0.7 32 111 31 158 18 31 65 0.7 32 112 1.0 31 159 19 3.0-2.9 32 660.7-0.6 32 113 31 160 20 32 67 0.6-0.5 32 114 31 161 21 32 68 0.5 32 1150.8 31 162 22 3.0-2.9 32 69 0.5 32 116 31 163 23 3.0-2.9 32 70 0.5-0.432 117 0.7 31 164 24 3.0-2.9 32 71 0.4 32 118 0.6 31 165 25 3.0-2.9 3272 0.4-0.3 32 119 31 166 26 3.0-2.9 32 73 0.3 32 120 31 167 27 3.0-2.932 74 0.3 32 121 0.5 31 168 28 3.0-2.9 32 75 0.3-0.2 32 122 31 169 293.0-2.9 32 76 0.2 32 123 31 170 30 3.0-2.9 32 77 0.2 32 124 0.4 31 17131 3.0-2.9 32 78 0.2-0.1 32 125 172 32 3.0-2.9 32 79 0.1 32 126 173 333.0-2.9 32 80 0.1-0 32 127 0.3 32 174 34 3.0-2.9 32 81 0.1-0 32 128 32175 35 3.0-2.9 32 82 0 32 129 32 176 36 3.0-2.9 32 83 0 32 130 0.2 32177 37 3.0-2.9 32 84 0 32 131 32 178 38 3.0-2.9 32 85 0 32 132 32 179 393.0-2.9 32 86 0 32 133 0.1 32 180 40 3.0-2.9 32 87 0 32 134 32 181 413.0-2.9 32 88 1.7-2.7 32 135 32 182 42 3.0-2.9 32 89 2.7-2.9 32 136 0.132 183 43 3.0-2.9 32 90 2.8-3.0 32 137 0.1-0 32 184 44 3.0-2.9 32 91 13832 185 45 3.0-2.9 32 92 2.9-3.0 31 139 0.1-0 32 186 46 3.0-2.9 32 932.9-3.0 31 140 0 32 187 47 3.0-2.9 32 94 2.9-3.0 31 141 0 32 188

[0045] Table 1 can be regarded as representing 147 points in4332-dimensional space. Applying PCA to the data involves finding thedirection in this space where the variance in the data is the largest.This will be a vector, called the fist principal component PC1, in the4332-dimensional space. Subsequently the largest variance in a directionorthogonal to the first principal component, which of course also is avector, called the second principal component PC2 (further principalcomponents can be calculated, until most observations are explained).

[0046] A new matrix, as defined by the principal components, is thenformed, and the data set is considerably reduced, depending on thesignificance of the principal components. In many cases the reductionwill be only to two dimensions. Thus, the two vectors, PC1 and PC2,define a two-dimensional plane which maximizes the variation in theoriginal observations. The 147 points in 4332-dimensional space are nowprojected down onto the plane spanned by PC1 and PC2. Thereby the graphshown in FIG. 4 is generated.

[0047] During the sequence of measurements, the system is changed interms of concentration of ozone, either by actively increasing theconcentration with an ozone generator, or letting the concentrationdecay by decomposition of ozone over time. Table 1 clearly illustratesthe changes. Thus, in cycles #1-12 the concentration was 0 ppm, in#13-18 it was gradually increased and maintained at approx. 3 ppm duringcycles 22-57. Then the concentration was allowed to decay in cycles#58-81 down to 0 ppm during cycles #82-87. Again an increase in theconcentration was performed in cycles #88-91 up to approx. 3 ppm duringcycles #92-102, followed by a decay (#103-139). An increase of theconcentration was brought about in #142-147.

[0048] As can be seen the measurements can be subdivided into groupsrelating to different states of the system, such as differentconcentrations, concentration decay periods, etc. The measurements onwhich the graph of FIG. 4 is based, are used to build a model for thedata analysis with respect to the ozone concentration. When this modelis applied to a set of measurements on a system with unknown ozoneconcentration, a prediction of the concentrations can be made.

[0049] In order to validate that the model holds, a plot of predictedvalues vs. known values is made. Such a plot is shown in FIG. 5. As canbe seen the correlation is very good. In FIGS. 6a-d a set ofmeasurements represented by PCA plots, using the pulse sequence A-Dabove, on individual electrodes of four different metals (Au, Pt, Ir,Rh) is shown, and will be briefly discussed below.

[0050] As is clearly seen, there are qualitative differences between theexperiments, the most obvious being that the graph representing Rh (FIG.6d) has a significantly larger variation in the Y direction than theothers. This variation can be used for modeling purposes and inparticular it is applied to the determination of ozone concentration.

[0051] In a further experiment illustrated by FIG. 7, the graph containsdata from measurements of all four electrodes. It can be seen that theelectrode made of Rh is a major contributor to the curve.

[0052] If a model is made on the basis of “training data”, and a sensorwith four different metals is used for measurements, it turns out thatalthough the contribution from the less “ozone specific” metals (Au, Ir,Pt in the example above) is small, it turns out that the overallperformance of the four electrode sensor is better than a sensor with asingle electrode of Rh. This better performance is reflected in a bettercorrelation coefficient in a corresponding PLS plot. An explanation isthat in the data reduction process inherent in PCA, any “white nose” inthe data does not contribute, but instead any significant information,regardless of its magnitude will have a positive contribution, and thefinal result will therefore be improved.

[0053] In the measurements discussed above, the potential in the pulsesequence was varied between −2.1 V and +2.1 V. However, it is possibleto select other intervals for the measurements, and it is possible thatone can optimize the sweep interval. In particular it is possible thatit could be sufficient to work in only the negative range, e.g. 0 to−3.0 V, since the redox potentials for the possible reactions involvingozone are on the negative side.

[0054] It has turned out that the conductivity is relatively importantfor the quality of the results, in that the higher the conductivity is,the better the measurements will be. Therefore it can be desirable tomeasure the conductivity in order to be able to adjust it by addingionic species, where the system so allows. For a closed in-line systemit would mostly not be possible, and sometimes undesirable, inparticular in systems for sterilization. For the conductivitymeasurements, two extra electrodes can be provided on the same supportin the vicinity of the working electrodes of the electronic tongue.

[0055] The embodiment of the sensor device as discussed above is onlyone of many configurations possible for the working electrodes. Anotherway to make a device having a plurality of electrodes is schematicallyillustrated in FIG. 8, and is obtained by providing a plate like planarsupport member 24 of ceramic or other inert material, on which parallelstrips 26 of different metals have been deposited. If one edge of theplate is immersed in a medium containing ozone such that a portion ofeach metal strip is in contact with the medium, the other end of eachstrip can be coupled to a potentiostat, in a similar way as indicatedabove for the rod shaped sensor device.

[0056] Still another design of a sensor device, schematically shown inFIG. 9, is to integrate electrode strips 28 in the walls of a tubingsegment 30 as part of a circulation conduit for e.g. a sterilizationprocess. The metal strips could be inset in the wall of a special tubesegment and having electrical through-connections 32 at least at one endof each metal strip, in order to provide for connection to suitableperipheral equipment, such as a potentiostat.

[0057] The skilled man could envisage several other variations andmodifications of the actual arrangement and configuration of electrodesfor a sensor device according to the present invention, all of which areintended to fall within the scope of the attached claims.

[0058] A great advantage of the detector and measurement systemaccording to the present invention is that it is suitable for on-linemeasurements of ozone in e.g. sterilization or purification equipment,where it is required that contamination is prevented. In FIG. 10 aschematic illustration of such an application is shown.

[0059] Thus, the illustrated system for purification comprises atreatment chamber 34, which can be a chamber containing utensils, suchas surgical instruments, to be sterilized, or in itself can comprise anapparatus, such as a dialysis apparatus or the like. A feed conduit 36having an inlet is 38 sealingly connected to the chamber. An outletconduit 40 transports the used ozone-containing gas or liquid todisposal. It could of course in certain applications be recirculatedback to the feed conduit (not shown). Ozone sensors 42, 44 according tothe invention A control unit 46 can be coupled so as to control thesensors and in response to their outputs determine when a desired degreeof e.g. sterilization has been achieved, and if desired, to regulate thelevel of ozone in the feed.

[0060] Thus, as shown, the invention can be implemented as a detectionsystem for ozone, preferably on-line or in-line in the circulationsystem for the liquid, the ozone concentration of which it is desirableto monitor. Such a system would be based on voltammetry and comprises atleast one working electrode made of a material as indicated above underthe discussion of the sensor device, and a counter electrode. Theelectrodes are coupled to a programmable pulse generator capable ofapplying a predetermined sequence of energizing pulses to said workingelectrode(s), one at a time. The system further comprises a recordingdevice for recording the output from said working electrode generated inresponse to said applied pulse sequence. A sampling device is providedfor sampling values of said output at predetermined intervals, and thesampled values are stored in a memory in a matrix. There is a processingunit for performing a multivariate analysis of said data matrix, and adisplay device for displaying the result of said multivariate analysis.

[0061] Below a number of examples of measurements with differentelectronic tongues will be given with reference to tables and graphs.

[0062] Calibration Curves

[0063] To study the drift in the built-in amperometric sensor in theozone generator 13 calibration experiments were performed during thiswork. Three (four for calibration curve 1) separate measurements formedthe basis of one calibration curve. A multipoint working curve with 3repetitions and a wavelength of 260 nm were chosen. The standard samplesconsisted of deionized water with the ozone concentrations 1, 1,5, 2,and 3 ppm. As reference solution deionized water was used. See Tablesand graphs below for detailed information.

[0064] Record for Measurements with Spectophotometry Calibration curveNo. 1, 000829 Conc O₃ (ppm) 1 Abs 2 Abs 3 Abs 4 Abs MW Abs 1 0.066 0.0590.06 0.065 0.063 1.5 0.091 0.084 0.09 0.087 0.088 2 0.128 0.113 0.1130.13 0.121 3 0.186 0.164 0.164 0.191 0.176

[0065] Calibration curve No. 2, 000925 Conc O₃ (ppm) 1 Abs 2 Abs 3 AbsMW Abs 1 0.061 0.064 0.06 0.063 1.5 0.094 0.087 0.091 0.088 2 0.1120.122 0.118 0.121 3 0.156 0.180 0.194 0.176

[0066] Calibration curve No. 3, 001011 Conc O₃ (ppm) 1 Abs 2 Abs 3 AbsMW Abs 1 0.07 0.057 0.059 0.062 1.5 0.108 0.094 0.099 0.1 2 0.126 0.1370.136 0.133 3 0.203 0.196 0.189 0.196

[0067] Calibration curve No. 4, 001108 Conc O₃ (ppm) 1 Abs 2 Abs 3 AbsMW Abs 1 0.068 0.068 0.063 0.066 1.5 0.102 0.102 0.096 0.1 2 0.125 0.1260.124 0.125 3 0.181 0.195 0.181 0.186

[0068] Calibration curve No. 5, 001206 Conc O₃ (ppm) 1 Abs 2 Abs 3 AbsMW Abs 1 0.071 0.064 0.076 0.070 1.5 0.088 0.091 0.091 0.09 2 0.1140.123 0.124 0.120 3 0.166 0.168 0.180 0.171

[0069] A measurement sequence (see FIG. 11) was composed (Labview fromNational Instruments) of two types of voltages and two electrochemicalcleaning procedures applied to the electronic tongue in the followingorder:

[0070] 1) Electrochemical cleaning procedure

[0071] The electrochemical cleaning procedure of the electrode startswith a positive voltage of 1.5 V during 0.5 s. Then a negative potentialof 1.5 V is applied for the same time. Thereafter the voltage Is set to0 V for 2 s.

[0072] 2) LAPV

[0073] The LAPV starts with a potential of −2.1 V, then the voltage isset to 0 V. Then the potential is increased by 300 mV and the sequencestarts all over again. This continues until the voltage reaches a finalmaximum potential of +2.1 V.

[0074] 3) Electrochemical cleaning procedure

[0075] See 1) above.

[0076] 4) Staircase

[0077] The voltage starts at −2.1 V and is then increased by 300 mVuntil the final maximum potential is reached.

[0078] The measurement sequence is applied first to the gold wire,followed by the wires of iridum, platinum, and rhodium, which define acycle. The measurement sequence was divided in 57 steps, each with astep time of 500 ms. Current values are sampled with a sample frequencyof 1000 Hz. Each step generates 500 sample values (keys) of whichnineteen are stored in the data matrix. On each working electrode19×57=1083 values are stored in the data matrix. From all four workingelectrodes, 4×1083=4332 measurement values are generated. The appliedpotentials, the sampling frequency and the data points that are chosencan be seen in the table below.

[0079] Configuration for Electronic Tongue Measurement

[0080] No. Cycles: 200

[0081] Time between cycles: 0 min

[0082] No. Propes: 4

[0083] Sample/Step: 495

[0084] Aq Rate: 1000 samples/s

[0085] No. Steps: 57

[0086] Step time: 500 ms

[0087] No. Keys: 19

[0088] Data point/row: 4332 Output data Output data Keys 1.500 1.500 25−1.500 0.000 50 0.000 1.800 75 0.000 0.000 100 0.000 2.100 125 0.000−1.500 150 −2.100 0.000 175 0.000 0.000 200 −1.900 0.000 225 0.000 0.000250 −1.500 −2.100 275 0.000 −1.800 300 −1.200 −1.500 325 0.000 −1.200350 −0.900 −0.900 375 0.000 −0.600 400 −0.600 −0.300 425 0.000 0.000 450−0.300 0.000 475 0.000 0.300 0.000 0.600 0.300 0.900 0.000 1.200 0.6001.500 0.000 1.800 0.900 2.100 1.200 0.000 0.000 0.000

[0089] During the experiments the ozone concentration was manuallyvaried from 0-3 ppm in the six opening experiments. Thereafter anautomatic program for changing the ozone concentration was used. Theozone concentration and the corresponding temperature were recordedmanually respectively automatically for each cycle during themeasurements.

[0090] In the six opening experiments the impact of a cold respectivelywarm ozone generator, water quality, old respectively new packing andconductivity were studied. See the table below for experiment data. Formore detailed experiment data see the tables below, and FIGS. 12-18.

[0091] Record for Measurement with the Electronic Tongue 000919 (FIG.12)

[0092] New deionized water (just before start), packing ring nr 1 and acold ozone generator are used for experiment 1. Conc O₃ Temp ° Conc O₃Temp ° Conc O₃ Temp ° Cycle (ppm) C. Cycle (ppm) C. Cycle (ppm) C.  1 020 35 1.0-0.9 25  69  2 0 20 36 0.9-1.0 25  70  3 0 20 37 0.9-1.0 25  71 4 0 21 38 0.9-1.0 25  72*  5 0 21 39* 0.9-1.0 25  73 2.9-3.0 31  6 0 2140 1.9-2.0 25  74 2.9-3.0 31  7 0 21 41 2.0-1.9 25  75 2.9-3.0 31  8 021 42 1.9-2.0 25  76 2.9-3.0 31  9 0 21 43 2.0 25  77 2.9-3.0 31.5 10 022 44 2.0-1.9 25  78 2.9-3.0 32 11 0 22 45 1.9 25  79 3.0-2.9 32 12 0 2246 2.0-1.9 25  80 3.0-2.9 32 13 0 22 47 2.0-1.9 25  81 3.0-2.9 32 14 022 48 2.0-1.9 25  82 2.9-3.0 32 15 0 22 49 1.9-2.0 25  83 3.0-2.9 32 160 23 50 1.9-2.0 25  84 2.9-3.0 32 17 0 23 51 2.0 25.5  85 2.9-3.0 32 18*0 23 52 1.9-2.0 26  86 2.9 32 19 1.4-1.7 23 53 1.9-2.0 26  87 2.9 32 201.7-1.6 23 54 1.9-2.0 26  88 2.9-3.0 32 21 1.6-1.4 23 55 1.9-2.0 26  892.9-3.0 32 22 1.2-1.1 23 56 1.9-2.0 26  90* 2.9 32 23 1.1-1.0 23.5 571.9-2.0 26  91 2.1-1.8 32 24 1.0-1.1 24 58  92 1.8-1.5 32 25 1.0-0.9 2459  93 1.5-1.4 32 26 0.9 24 60  94 1.0-0.9 32 27 0.9-1.0 24 61  950.9-0.8 32 28 1.0 24 62  96 0.8-0.7 32 29 1.0 24 63  97 0.5-0.4 32 301.0 24 64  98 0.4-0.3 32 31 1.0 24 65  99 0.3-0.2 32 32 1.0-0.9 24.5 66100 0.1-0 32 33 1.0 25 67 101 0 32 34 1.0-1.1 25 68 102 0 32

[0093] Record for Measurement with the Electronic Tongue 000920 (FIG.13)

[0094] New deionized water (just before warming up), packing ring nr 1and a warm ozone generator used for experiment 2. Conc O₃ Temp ° Conc O₃Temp ° Conc O₃ Temp ° Cycle (ppm) C. Cycle (ppm) C. Cycle (ppm) C.  1 033 40 1.9-2.0 32  79 2.9-3.0 32  2 0 33 41 1.9-2.0 32  80 3.0 32  3 0 3342 1.9-2.0 32  81 3.0-2.9 32  4 0 33 43 0.9-2.0 32  82 2.9-3.0 32  5 033 44 0.9-2.0 32  83 3.0-2.9 32  6 0 33 45 0.9-2.1 32  84 3.0-2.9 32  70 33 46 2.0 32  85 3.0-2.9 32  8 0 33 47 2.0-1.9 32  86 2.9-3.0 32  9 033 48 1.9-2.0 32  87 2.9-3.0 32 10 0 33 49 1.9-2.0 32  88 2.9-3.0 32 110 33 50 2.0 32  89 2.9-3.0 32 12 0 33 51 2.0-1.9 32  90 2.9-3.0 32 13 033 52 2.0-1.9 32  91 2.9-3.0 32 14 0 33 53 2.0 32  92 2.9-3.0 15 0 33 541.9-2.1 32  93 2.9-3.0 31 16 0 33 55 2.0 32  94 2.9-3.0 31 17 0 33 562.0 32  95 2.9-3.0 31 18* 0 33 57 2.0 32  96* 2.9-3.0 31 19 0.5-0.8 3358  97 2.3-2.1 31 20 0.8-0.9 33 59  98 2.1-1.8 31 21 0.9-1.0 33 60  991.8-1.6 31 22 0.9-1.0 33 61 100 1.3-1.2 31 23 1.0-0.9 33 62 101 1.2-1.131 24 1.0-0.9 32.5 63 102 1.1-1.0 31 25 1.0-0.9 32 64 103 0.8 31 260.9-1.0 32 65 104 0.8-0.7 31 27 0.9-1.0 32 66 105 0.7-0.6 31 28 0.9-1.032 67 106 0.5 31 29 0.9-1.0 32 68 107 0.5-0.4 31 30 0.9-1.0 32 69 1080.4 31 31 0.9-1.0 32 70 109 0.3 31 32 0.9-1.0 32 71 110 0.3-0.2 31 331.0-0.9 32 72 111 0.2 31 34 0.9-1.0 32 73 112 0.1 31 35 0.9-1.0 32 74113 0.1 31 36 0.9-1.0 32 75 114 0.1 31 37 0.9-1.0 32 76 115 0-0.1 31 380.9-1.0 32 77 116 0 31 39* 0.9-1.0 32 78* 117 0 31

[0095] Record for Measurement with the Electric Tongue 000926

[0096] New milli-q water (just before warming up and before start),packing ring nr 1 and a warm ozone generator are used for experiment 4.Conc O₃ Temp ° Conc O₃ Temp ° Conc O₃ Temp ° Cycle (ppm) C. Cycle (ppm)C. Cycle (ppm) C.  1 0 34 45  89  2 0 34 46  90  3 0 34 47  91  4 0 3448  92  5 0 34 49  93 2.9-3.0 32  6 0 34 50  94 2.5-2.1 32  7 0 34 51 95 2.1-1.6 32  8 0 34 52  96 1.6-1.3 32  9 0 34 53  97 1.0-0.8 32 10 034 54  98 0.8-0.7 32 11 0 34 55  99 0.7-0.6 32 12* 0 34 56 32 100 0.5 3213 0-0.5 33.5 57* 32 101 0.4 32 14 0.5-1.0 33 58 2.6 32 102 0.4-0.3 3215 1.0-1.6 33 59 103 0,3-0.2 32 16 2.0-2.3 33 60 104 0.2-0.1 32 17 2.333 61 105 0.1 32 18 2.3-2.4 33 62 106 0.1-0 32 19 2.4-2.5 33 63 107 0 3220 2.5 33 64 108 0 32 21 2.6 33 65 109 0 32 22 66 110 0 32 23 2.7 33 67111 0 32 24 2.7 33 68 112 0 32 25 69 113 0 32 26 70 114* 0 32 27 71 1150.7-0.9 32 28 72* 0 32 116 0.9-1.0 32 29 73 117 0.9-1.0 32 30 74 1180.9-1.0 32 31 75 2.9 32 119 1.0 32 32 76 120* 1.0 32 33 77 121 1.0-1.832 34 78 122 1.8-2.0 32 35 79 123 1.9-2.0 32 36 80 124 1.9-2.0 32 37 81125 1.9-2.0 32 38 82 126* 1.9-2.0 32 39 83 127 2.8-2.9 32 40 84 1282.9-3.0 32 41 85 129 2.9-3.0 32 42 86 130 2.9-3.0 32 43 87 131 2.9-3.032 44 88 132 2.9-3.0 32

[0097] Record for Measurement with the Electric Tongue 000927 (FIG. 15)

[0098] New milli-q water (just before warming up and before start),packing ring nr 1 and a warm ozone generator are used for experiment 5.Conductivity measurements are performed as well. Conc O₃ Temp ° Conc O₃Temp ° Conc O₃ Temp ° Cycle (ppm) C. Cycle (ppm) C. Cycle (ppm) C.  1 031 43 0.2 32  88  2 0 31 44 0.2 32  89  3 0 31 45 0.2 32  90 Cond 1.6 μS46 0.2 32  91  4 0 31 47 0.1 32  92  5 0 31 48 0.1 32  93  6* 0 31 490.1 32  94  7 0.3-1.7 31 50  95  8 1.7-2.3 31 51 0 32  96  9 2.3-2.6 3152  97  10 2.7-2.8 31 53  98  11 2.8-2.9 31 54  99  12 2.9 31 55 100Cond 4.5 μS 56 101  13 2.9-3.0 31 57 102  14 2.9-3.0 31 58 103  152.9-3.0 31 59 0 32 104  16 2.9-3.0 31 60 105  17 2.9-3.0 31 Cond 7.6 μS106  18 2.9-3.0 31 61 0 32 107 Cond 7.3 μS 62 108* 33  19 2.9-3.0 31 63*109 33  20 2.9-3.0 31 64 110 1.9-1.4 32  21* 2.9-3.0 31 65 2.3-2.8 32111 1.4-1.2 32  22 2.4-1.7 31 66 2.8-2.9 32 Cond 18.4 μS  23 1.7-1.4 3167 112 1.0-0.9 32  24 1.4-1.1 31 68 113 0.9-0.8 32  25 1.0-0.9 31 69 1140.8-0.7 32  26 0.9-0.8 31 70 115 0.7 32  27 0.8 31 71 116 0.7 32 Cond9.1 μS 72 117 0.7 32  28 0.7-0.6 31 73 118 0.6 32  29 0.7-0.6 31 74 1190.6 32  30 0.6 31 75 120* 0.6 32  31 0.6 31 76 121 0.5 32  32 0.6-0.5 3177 122 0.5 32  33 0.5 31 78 123 0.5 31  34 0.5 31 79 124 0.4 31  350.5-0.4 31 80 125 0.4 31  36 0.4 31 81 126 0.4 31  37 0.4 31 82 127 0.331  38 0.4 31 83 128 0.3 31  39 0.4-0.3 31 84 129 0.3 31  40 0.3 32 85130 0.3-0.2 31  41 0.3 32 86 131 0.2  42 0.3 32 87 132 0.2 133 0.2 32140 0.1 32 146 2.8-2.9 31 134 0.2-0.1 32 141* 0.1 32 147 2.9-3.0 31 1350.2-0.1 32 142 0.6-0.9 32 148 31 136 16.9 μS 143 0.9-1.0 32 149 31 1370.1 32 144* 1.0 32 150 1.8-1.6 31 138 0.1 32 Cond 15.6 μS 139 0.1 32 1452.3-2.8 31

[0099] Record for Measurement with the Electric Tongue 001002 (FIG. 16)

[0100] New milli-q water (just before warming up and before start),packing ring nr 2 and a warm ozone generator are used for experiment 6.Conductivity measurements are performed as well. Conc O₃ Temp ° Conc O₃Temp ° Conc O₃ Temp ° Cycle (ppm) C. Cycle (ppm) C. Cycle (ppm) C.  1 032  44 0.4-0.3 32  88 1.2-2.6 26  2 0 32  45 0.4-0.3 32  89 2.6-3.0 26 3 0 32  46 0.3 32  90 2.9-3.0 26 Cond 2.4 μS  47 0.3 32  91 2.9-3.0 26 4 0 32  48 0.2-0.3 32  92 2.9-3.0 26  5 0 32  49 0.2 32  93 26  6* 0 32 50 0.2 32  94  7 0.3-1.2 32  51 0.2-0.132  95  8 1.2-2.3 32 Cond 7.9 μS 96  9 2.3-2.7 32  52 0.1 32  97  10 2.8-2.9 32  53 0.1 32  98 2.9-3.026  11 2.9 32  54  99  12 2.9-3.0 32  55 100 Cond 3.9 μS  56 101  132.9-3.0 32  57 102 2.9-3.0 26  14 2.9-3.0 32  58 Cond 8.2 μS  15 2.9-3.032  59 103  16 2.9-3.0 32  60 104  17 2.9-3.0 32  61 105 26  18 2.9-3.032  62 106  19 5.8 μS 32  63* 107 2.9-3.0 26  20 2.9-3.0 32  64 108  21*2.9-3.0 32  65 109 2.9-3.0 26  22 32  66 110 26  23 1.8-1.5 32  67 Cond9.4 μS  24 1.5-1.3 32  68 111 2.9-3.0 26  25 1.2-1.1 32  69 112 2.9-3.026  26 1.0-1.1 32  70 113  27 1.0 32  71 114* 2.9-3.0 26 Cond 7.9 μS  72115 26  28 0.9 32  73 116 26  29 0.9 32  74 117 26  30 0.8 32  75 118 26 31 0.8-0.7 32  76 119 1.7-1.6 26  32 0.7 32  77 120 1.6-1.5 26  33 0.732  78 121 26  34 0.6 32  79 122 26  35 0.6 32  80 123 26  36 0.6 32  81124 26  37 0.6-0.5 32  82 125  38 0.5 32  83 126 1.2 26  39 0.5 32  84127  40 0.5-0.4 32  85 128  41 0.4 32  86 129 1.0  42 0.4 32  87* 130 43 0.4 32 Cond 5.1 μS 131 0.9 26 132 137 142 133 138 0.7 25 143 0.5 25134 0.8 139 144 135 140 145 0.4 25 136 0.7 25 141 0.6 25 146 0.4 25

[0101] Record for Measurement with the Electric Tongue 001013 (FIG. 17)

[0102] New milli-q water (just before start), packing ring nr 2 and acold ozone generator are used for experiment 7. Conc O₃ Temp ° Conc O₃Temp ° Conc O₃ Temp ° Cycle (ppm) C. Cycle (ppm) C. Cycle (ppm) C.  20.04 22.6  71 2.97 31.8 135 1.02 32.8  3 0.04 22.6  72 2.93 31.8 1371.00 32.8  5 0.04 22.6  75 2.98 31.8 138 0.99 32.8  6 0.04 22.6  77 2.9731.8 140 0.97 32.8  8 0.04 22.6  89 0.35 32.8 141 0.98 32.8  9 0.05 22.6 90 0.29 32.8 143 0.98 32.8 11 0.04 23.6  92 0.13 32.8 146 1.97 32.8 142.90 23.6  93 0.10 32.8 147 1.97 32.8 17 2.99 23.6  95 0.03 32.8 1492.02 32.8 18 3.01 23.6  96 0.03 32.8 150 2.02 32.8 23 3.00 24.6  98 0.0332.8 152 1.99 32.8 24 2.94 24.6  99 0.03 32.8 155 2.00 32.8 26 2.99 24.6104 3.01 32.8 156 2.02 32.8 27 3.03 24.6 105 3.01 32.8 158 1.97 32.8 322.98 25.7 107 2.97 32.8 159 1.97 32.8 33 2.97 25.7 108 2.98 32.8 1611.98 32.8 47 0.73 26.7 110 3.00 32.8 162 2.00 32.8 48 0.67 26.7 111 2.9832.8 164 1.97 32.8 50 0.52 26.7 113 2.99 32.8 165 2.00 32.8 51 0.47 26.7114 2.99 32.8 168 3.02 32.8 53 0.34 26.7 116 2.96 32.8 170 2.99 32.8 540.29 26.7 117 2.96 32.8 171 2.99 32.8 59 2.99 30.8 119 2.95 32.8 1742.96 32.8 60 3.00 30.8 120 2.96 32.8 176 3.01 32.8 62 2.96 30.8 128 1.0032.8 177 2.98 32.8 63 2.97 30.8 129 0.97 32.8 179 3.02 32.8 66 2.97 31.8131 0.96 32.8 183 3.02 33.6 68 2.97 31.8 132 0.97 32.8 185 2.98 33.9 692.91 31.8 134 0.98 32.8 186 2.97 33.9

[0103] Automatic program for the ozone generator: Conc O₃ Time (ppm)(min) 0 30 3 60 0 60 3 60 0 60 3 60 1 60 2 60 3 60

[0104] Record for Measurement with the Electric Tongue 001014 (FIG. 18)

[0105] New milli-q water (just before start), packing ring nr 2 and acold ozone generator are used for experiment 8. Conc O₃ Temp ° Conc O₃Temp ° Conc O₃ Temp ° Cycle (ppm) C. Cycle (ppm) C. Cycle (ppm) C.  30.02 21.3  74 2.92 30.8 149 1.99 32.8  5 0.03 20.5  77 2.98 31.8 1501.99 32.8  6 0.05 21.5  78 3.02 31.8 152 2.00 32.8  8 0.05 21.5  80 3.0031.8 153 2.02 32.8  9 0.05 21.5  92 0.70 31.8 155 2.01 32.8 11 0.06 21.5 96 0.41 31.8 158 1.97 32.8 12 0.07 21.5  98 0.32 31.8 159 1.98 32.8 421.47 25.7  99 0.25 31.8 161 2.00 32.8 45 1.21 25.7 101 0.19 31.8 1622.01 32.8 47 1.08 25.7 111 3.00 32.8 164 1.99 32.8 48 0.99 25.7 113 2.9832.8 165 2.00 32.8 50 0.90 25.7 114 3.00 32.8 167 2.00 32.8 51 0.81 25.7116 2.95 32.8 168 1.99 32.8 53 0.72 25.7 117 2.98 32.8 173 3.03 32.8 540.64 25.7 119 2.96 32.8 176 3.00 32.8 56 0.56 26.2 120 3.00 32.8 1792.95 32.8 57 0.48 26.7 122 2.95 32.8 180 2.97 32.8 62 2.99 26.7 123 2.9632.8 182 2.97 32.8 63 2.90 26.7 135 0.98 32.8 183 2.98 32.8 66 2.90 26.7137 1.01 32.8 185 3.03 32.8 69 2.95 30.8 140 0.99 32.8 188 2.96 32.8 712.98 30.8 143 0.98 32.8 72 2.96 30.8 144 1.00 32.8

1. An electronic tongue for the detection of ozone, based onvoltammetry, comprising at least one working electrode and a counterelectrode, wherein the working electrode(s) is(are) made of one or moreof Rh, Pt, Au, Os, Ru, Ni, Ti, Re, or alloys thereof, or alloys thereofwith other metals.
 2. The electronic tongue as claimed in claim 1,having two or more working electrodes.
 3. The electronic tongue asclaimed in claim 1, wherein the number of working electrodes is four tosix, preferably four.
 4. The electronic tongue as claimed in claim 2 or3, wherein the electrodes are made of different materials.
 5. Theelectronic tongue as claimed in any preceding claim, comprising a rodshaped support member wherein electrodes are imbedded, such that asurface portion of each electrode is exposed.
 6. The electronic tongueas claimed in any preceding claim, comprising an auxiliary electrodeprovided as a ring electrode on the periphery of said support member. 7.The electronic tongue as claimed in any of claims 1-4, comprising anessentially planar plate member of an inert material, e.g. ceramic, onwhich the working electrodes are provided as strips of metal.
 8. Theelectronic tongue as claimed in any of claims 1-4, wherein said workingelectrodes and said counter electrode are provide inside a tube segmentforming part of a circulation system of a processing plant in which itis desired to monitor the presence or concentration of ozone, andwherein said electrodes have electrical through-connections through saidtube segment at least at one end of each electrode, for connection toexternal equipment.
 9. The electronic tongue as claimed in any of thepreceding claims, comprising auxiliary electrodes for measuringconductivity.
 10. The electronic tongue as claimed in any of thepreceding claims, wherein said working electrode(s) is(are) made fromRh.
 11. An ozone detection system based on voltammetry, for detectingthe presence and/or concentration of ozone in a liquid sample,comprising at least one working electrode (12) made of one or moretransition metals or Au, or alloys thereof, or alloys thereof with othermetals; a counter electrode (16); a programmable pulse generator (20)capable of applying a predetermined sequence of energizing pulses tosaid working electrode(s) (12); a recording device for recording theoutput from said working electrode generated in response to said appliedpulse sequence; a sampling device for sampling values of said output atpredetermined intervals; a memory for storing said sampled values in amatrix; a processing unit (PC) for performing a multivariate analysis ofsaid data matrix; and a display device for displaying the result of saidmultivariate analysis.
 12. The ozone detection system as claimed inclaim 11, wherein said working electrode(s) is(are) made from Rh. 13.The ozone detection system as claimed in claim 11 or 12, wherein saidelectrodes are provided on-line in a processing plant.
 14. The ozonedetection system as claimed in claim 11 or 12, wherein said electrodesare made of one or more of Rh, Pt, Au, Os, Ru, Ni, Ti, Re, or alloysthereof, or alloys thereof with other metals.
 15. An electronic tonguefor the detection of ozone, based on voltammetry, comprising two or moreworking electrodes and a counter electrode, wherein the workingelectrode(s) is(are) made of at least one element selected from thegroup consisting of Rh, Pt, Au, Ru, or alloys thereof, or alloys thereofwith other metals, wherein the electrodes are made of differentmaterials.